1. Field of the Invention
The invention relates to a power semiconductor device; in particular, to a power semiconductor device of stripe cell geometry.
2. Description of the Prior Art
The power semiconductor device has become an important power control product due to its advantages of lower switching loss and simple driving circuit and rapid development of semiconductor manufacturing process technologies. The power semiconductor devices can be divided into trench gate power semiconductor devices and planar gate power semiconductor devices according to their different channel positions. The channel of the trench gate power semiconductor device is disposed along a direction vertical to the chip surface; the channel of the trench gate power semiconductor devices is disposed along a direction parallel to the chip surface. The power semiconductor devices can be also divided into squared cells and striped cells according to their different cell designs. The squared cell design and striped cell design both have their own advantages. In general, the squared cell design can have lower conductive resistance and the striped cell design can provide better Miller capacitance.
FIG. 1A illustrates a schematic diagram of a conventional power semiconductor device. As shown in FIG. 1A, a gate metal pad G and a source metal pad S are disposed on the upper surface of the power semiconductor device, and a drain metal pad (not shown in FIG. 1A) is disposed on the lower surface of the power semiconductor device. The upper surface of the power semiconductor device can be divided into an active area A1 and a termination area A2. Many power semiconductor units (cells) are located in the active area A1.
FIG. 1B and FIG. 1C illustrate schematic diagrams of the active area A1 of the power semiconductor device. In FIG. 1B and FIG. 1C, a striped cell power semiconductor device is taken as an example, and the gate metal pad G and the source metal pad S are omitted to show the striped cell in the active area A1. As shown in FIG. 1B, there are many striped gate conductive structures 12 in the active area A1, and each of the striped gate conductive structures 12 corresponds to a power semiconductor cell. The power semiconductor device has a ring-shaped conductive structure 22 surrounding the active area A1. Two ends of the striped gate conductive structure 12 are connected to the ring-shaped conductive structure 22 to obtain gate voltage for operation. FIG. 1C illustrates the distribution of the body-doped region defined by the conductive structure of FIG. 1A including the striped gate conductive structure 12 and the ring-shaped conductive structure 22. It should be noticed that the body-doped region in the active area A1 will be divided into many striped body-doped regions 14 due to the existence of the striped gate conductive structure 12. There are different distances t1 and t2 between the ends of the striped body-doped regions 14 and adjacent doped regions 24; therefore, the distribution of the electrical field around the active area A1 will be non-uniform and the performance of the power semiconductor device will become poor.
FIG. 1D and FIG. 1E illustrate schematic diagrams of the termination area A2 of the power semiconductor device. Similarly, the gate metal pad G and the source metal pad S located at the top of the chip are also omitted. As shown in FIG. 1D and FIG. 1E, there is a guard ring structure disposed in the termination area A2 of the power semiconductor device to increase the break-down voltage of the power semiconductor device. The guard ring structure includes a poly-silicon terminal pattern. The poly-silicon terminal pattern includes a poly-silicon gate bus 26 and ring-shaped poly-silicon structures 22. The ring-shaped poly-silicon structures 22 extend from two sides of the poly-silicon gate bus 26 to surround the active area A1. The poly-silicon terminal pattern defines the doped regions 24 in the substrate and the doped regions 24 surround the active area A1 in order. It should be noticed that each doped region 24 has a breach corresponding to the poly-silicon gate bus 26 due to the existence of the poly-silicon gate bus 26; therefore, voltage tolerance of the guard ring structure will be affected, and the break-down voltage of the power semiconductor device will also become smaller.